The hydraulic brakes used for braking the wheels of aircraft generally comprise a ring having multiple cavities in which brake actuators are housed removably. Each of the actuators comprises a liner which is sealingly added to one of the cavities of the ring and in which a piston is mounted to slide sealingly along an axis of sliding. The ring distributes hydraulic fluid under pressure to all its cavities, which fluid acts on the piston in order to cause it to deploy and apply a braking force to friction pads extending opposite the ring, rotors of which rotate with the wheels and stators of which are prevented from rotating.
In general, the piston has an operational travel that it covers when a braking force is applied. This operational travel, of the order of a few millimeters, is enough to allow the braking force to be applied to the friction pads and to cause the push-rod to retreat to allow the rotors to rotate freely. To this end, a spring extending inside the piston ensures that the push-rod retreats into a retracted position when the braking force is no longer applied.
However, the friction pads gradually become worn as a result of repeated application of braking forces so it is important to ensure that the piston is always near the friction pads. In order to achieve this it is known practice to fit the brake actuators with a wear compensation device that extends inside the piston. The wear compensation device comprises a mobile stop which is mounted to slide with friction along the axis of sliding on a central rod extending into the piston and which defines the position to which the piston retreats.
When a braking force is applied, the piston is pushed towards the friction pads and, if necessary, carries the mobile stop along with it, overcoming the friction between the rod and the stop, thereby causing the mobile stop to move forward along the central rod. When the force is released, the spring, which extends between the mobile stop and the piston, causes the piston to retreat as far as the new retracted position, which has moved forward because the mobile stop has moved forward.
There is known, from FR2820794, a brake actuator which is illustrated in FIG. 6B, in which the wear compensation device comprises a mobile stop (182, 184) whose friction member (the friction rings 182) acts directly on the wall of the liner.